Vehicular control object determination system and vehicular travel locus estimation system

ABSTRACT

In a vehicular control object determination system, locus correlation degree calculator calculates a degree of correlation between a future travel locus of a vehicle estimated by first travel locus estimator based on a vehicle speed and a yaw rate and a future travel locus of the vehicle estimated by second travel locus estimator based on a past travel locus of the vehicle calculated by travel locus calculator. When control object determiner determines a control object based on the travel locus estimated by the first travel locus estimator and predetermined control object determination conditions, the control object determination conditions are modified according to the degree of correlation, that is, the degree of reliability of the travel locus estimated by the first travel locus estimator, thereby achieving both accuracy with which the control object is determined and determination of the control object at a distance.

RELATED APPLICATION DATA

The present application claims priority to Japanese priority applicationNos. 2004-270894 and 2004-297151, filed Sep. 17, and Oct. 12, 2004,respectively, which are hereby incorporated in their entirety herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vehicular control objectdetermination system that includes an object detector for detecting anobject that is present in the direction of travel of a vehicle, avehicle speed sensor for detecting a vehicle speed, a yaw rate sensorfor detecting a yaw rate, a first travel locus estimator for estimatinga future travel locus of the vehicle based on the vehicle speed detectedby the vehicle speed sensor and the yaw rate detected by the yaw ratesensor, and a control object determiner for determining a control objectbased on a detection result obtained by the object detector, the travellocus estimated by the first travel locus estimator, and predeterminedcontrol object determination conditions.

The present invention also relates to a vehicular travel locusestimation system that includes a vehicle speed sensor for detecting avehicle speed, a yaw rate sensor for detecting a yaw rate, a firsttravel locus estimator for estimating a future travel locus of thevehicle based on the vehicle speed detected by the vehicle speed sensorand the yaw rate detected by the yaw rate sensor, and an estimatedtravel locus output providing an estimated travel locus.

2. Description of the Related Art

Japanese Patent Application Laid-open No. 2004-110390 discloses a systemin which, in order to estimate a future travel path of a subjectvehicle, a first subject vehicle travel path is estimated based on roadinformation, a second subject vehicle travel path is estimated based onthree-dimensional object information, a third subject vehicle travelpath is estimated based on running conditions of the subject vehicle, anew subject vehicle travel path is calculated from these first to thirdsubject vehicle travel paths, and a final subject vehicle travel path iscalculated from a previously calculated subject vehicle travel path anda currently calculated subject vehicle travel path.

However, in this conventional arrangement, it is necessary to add newdetection means such as a camera in order to estimate the subjectvehicle travel path based on road information and three-dimensionalobject information, and further there is a case where a lane, which isprimary road information, cannot be detected with good accuracy at nightor when it is raining, snowing, etc., leading to a possibility that itbecomes impossible to secure the accuracy with which the subject vehicletravel path is calculated. Furthermore, since the final subject vehicletravel path is calculated from the previously calculated subject vehicletravel path and the currently calculated subject vehicle travel path,there is a possibility that a time delay might occur in obtaining thefinal subject vehicle travel path by calculation, and the timing ofidentification of an object such as a preceding vehicle might bedelayed.

Japanese Patent Application Laid-open No. 2002-319100 discloses a systemin which a vehicle travel locus is estimated based on a yaw rate and avehicle speed; when it is determined that the vehicle has shifted from atraveling state to a stationary state, an estimated travel locus priorto becoming stationary is kept, thereby estimating a travel locus when avehicle that has stopped partway through a corner starts traveling.

However, when the vehicle speed is low, the output of the yaw ratesensor is unstable, and the accuracy with which the yaw rate is detectedis degraded. Therefore, the reliability of the yaw rate detectedimmediately before the vehicle stops is low, and thus the reliability ofthe travel locus immediately before the vehicle stops, which isestimated based on the yaw rate, is also low. Consequently, even if anattempt is made to estimate the travel locus after the vehicle startsusing this low reliability travel locus, there is a limit to theaccuracy of the estimated travel locus.

SUMMARY OF THE INVENTION

The present invention has been accomplished under the above-mentionedcircumstances, and it is a first object thereof to appropriatelydetermine a control object, such as a preceding vehicle, for controllingthe travel of a subject vehicle.

Furthermore, it is a second object of the present invention to estimatea travel locus with good accuracy when a vehicle that has stopped startstraveling.

In order to achieve the first object, according to a first feature ofthe present invention, there is provided a vehicular control objectdetermination system comprising: an object detector for detecting anobject that is present in the direction of travel of a vehicle; avehicle speed sensor for detecting a vehicle speed; a yaw rate sensorfor detecting a yaw rate; a first travel locus estimator for estimatinga future travel locus of the vehicle based on the vehicle speed detectedby the vehicle speed sensor and the yaw rate detected by the yaw ratesensor, a control object determiner for determining a control objectbased on a detection result obtained by the object detector, a travellocus estimated by the first travel locus estimator, and predeterminedcontrol object determination conditions; a travel locus calculator forcalculating a past travel locus of the vehicle; a second travel locusestimator for estimating a future travel locus of the vehicle based onthe calculated past travel locus; and a locus correlation degreecalculator for determining a degree of correlation between the travellocus estimated by the first travel locus estimator and the travel locusestimated by the second travel locus estimator; the control objectdeterminer modifying the control object determination conditions basedon an output of the locus correlation degree calculator.

With this arrangement, the locus correlation degree calculatorcalculates the degree of correlation between the future travel locus ofthe vehicle estimated by the first travel locus estimator based on thevehicle speed and the yaw rate, and the future travel locus of thevehicle estimated by the second travel locus estimator based on the pasttravel locus of the vehicle calculated by the travel locus calculator,and when determining a control object based on the travel locusestimated by the first travel locus estimator and the predeterminedcontrol object determination conditions, the control object determinermodifies the control object determination conditions according to thedegree of correlation, that is, according to the degree of reliabilityof the travel locus estimated by the first travel locus estimator.Therefore, it is possible to achieve both accuracy with which thecontrol object is determined and determination of the control object ata distance.

According to a second feature of the present invention, in addition tothe first feature, the control object determiner determines as a controlobject an object detected by the object detector if the relativedistance between the position of the object and the travel locusestimated by the first travel locus estimator is equal to or less than apredetermined value, and modifies, based on the degree of correlationcalculated by the locus correlation degree calculator, the effectivelength of the travel locus estimated by the first travel locusestimator.

With this arrangement, when determining an object detected by the objectdetector as the control object if the relative distance between theposition of the object and the travel locus estimated by the firsttravel locus estimator is equal to or less than the effective detectiondistance, the effective length of the estimated travel locus is modifiedaccording to the degree of reliability of the travel locus estimated bythe first travel locus estimator. Therefore, it is possible to determinea control object up to the maximum distance while securing the accuracywith which the control object is determined.

According to a third feature of the present invention, in addition tothe second feature, the control object determiner increases theeffective length of the estimated travel locus when the degree ofcorrelation calculated by the locus correlation degree calculator isequal to or greater than a predetermined value.

With this arrangement, the effective length of the estimated travellocus is increased when the degree of correlation is equal to or greaterthan the predetermined value. Therefore, it is possible to determine acontrol object up to the maximum distance when the degree of reliabilityof the travel locus estimated by the first travel locus estimator ishigh.

According to a fourth feature of the present invention, in addition tothe second or third feature, the control object determiner reduces theeffective length of the estimated travel locus when the degree ofcorrelation calculated by the locus correlation degree calculator isless than a predetermined value.

With this arrangement, the effective length of the estimated travellocus is reduced when the degree of correlation is less than thepredetermined value. Therefore, it is possible to prevent erroneousdetermination of a control object when the degree of reliability of thetravel locus estimated by the first travel locus estimator is low.

According to a fifth feature of the present invention, in addition tothe first feature, the control object determiner determines as a controlobject an object detected by the object detector if the distance betweenthe subject vehicle and the position of the object is equal to or lessthan an effective detection distance, and modifies the effectivedetection distance based on the degree of correlation calculated by thelocus correlation degree calculator.

With this arrangement, when determining an object detected by the objectdetector as the control object if the distance between the position ofthe object and the subject vehicle is equal to or less than theeffective detection distance, the effective detection distance ismodified according to the degree of reliability of the travel locusestimated by the first travel locus estimator. Therefore, it is possibleto determine a control object up to the maximum distance while securingthe accuracy with which the control object is determined.

According to a sixth feature of the present invention, in addition tothe fifth feature, wherein the control object determiner increases theeffective detection distance when the degree of correlation calculatedby the locus correlation degree calculator is equal to or greater than apredetermined value.

With this arrangement, the effective detection distance is increasedwhen the degree of correlation is equal to or greater than thepredetermined value. Therefore, it is possible to determine a controlobject up to the maximum distance when the degree of reliability of thetravel locus estimated by the first travel locus estimator is high.

According to a seventh feature of the present invention, in addition tothe fifth or sixth feature, the control object determiner reduces theeffective detection distance when the degree of correlation calculatedby the locus correlation degree calculator is less than a predeterminedvalue.

With this arrangement, the effective detection distance is reduced whenthe degree of correlation is less than the predetermined value.Therefore, it is possible to prevent erroneous determination of acontrol object when the degree of reliability of the travel locusestimated by the first travel locus estimator is low.

According to an eighth feature of the present invention, in addition tothe first feature, the locus correlation degree calculator calculates adegree of correlation based on a difference between the travel locusestimated by the first travel locus estimator and the travel locusestimated by the second travel locus estimator.

With this arrangement, the degree of correlation is calculated based onthe difference between the travel locus estimated by the first travellocus estimator and the travel locus estimated by the second travellocus estimator. Therefore, it is possible to calculate the degree ofcorrelation with good accuracy.

According to a ninth feature of the present invention, in addition tothe first feature, the locus correlation degree calculator calculatesthe degree of correlation based on a degree of similarity intwo-dimensional shape between the travel locus estimated by the firsttravel locus estimator and the travel locus estimated by the secondtravel locus estimator.

With this arrangement, the degree of correlation is calculated based onthe degree of similarity in two-dimensional shape between the travellocus estimated by the first travel locus estimator and the travel locusestimated by the second travel locus estimator. Therefore, it ispossible to calculate the degree of correlation with good accuracy.

According to a tenth feature of the present invention, in addition tothe first feature, the locus correlation degree calculator calculatesthe degree of correlation based on a difference between a turning radiusof the travel locus estimated by the first travel locus estimator and aturning radius of the travel locus estimated by the second travel locusestimator.

With this arrangement, the degree of correlation is calculated based onthe difference between the turning radius of the travel locus estimatedby the first travel locus estimator and the turning radius of the travellocus estimated by the second travel locus estimator. Therefore, it ispossible to calculate the degree of correlation with good accuracy.

In order to achieve the second object, according to an eleventh featureof the present invention, there is provided a vehicular travel locusestimation system comprising: a vehicle speed sensor for detecting avehicle speed; a yaw rate sensor for detecting a yaw rate; first travellocus estimator for estimating a future travel locus of the vehiclebased on the vehicle speed detected by the vehicle speed sensor and theyaw rate detected by the yaw rate sensor; estimated travel locus outputproviding an estimated travel locus; travel locus calculator forcalculating a past travel locus of the vehicle; and second travel locusestimator for estimating a future travel locus of the vehicle based onthe calculated past travel locus; the estimated travel locus outputproviding the travel locus estimated by the second travel locusestimator when the vehicle speed detected by the vehicle speed sensor isequal to or less than a predetermined value and a change per unit timein the yaw rate detected by the yaw rate sensor is equal to or greaterthan a predetermined value.

With this arrangement, when the vehicle speed detected by the vehiclespeed sensor is equal to or less than the predetermined value, and thechange per unit time in yaw rate detected by the yaw rate sensor isequal to or greater than the predetermined value, that is, when thereliability of the yaw rate outputted by the yaw rate sensor is low, theestimated travel locus output does not provide a future travel locus ofthe vehicle estimated by the first travel locus estimator using the yawrate, but instead provides a future travel locus of the vehicleestimated by the second travel locus estimator based on the past travellocus of the vehicle calculated by the travel locus calculator.Therefore, it is possible to enhance the accuracy of the future travellocus outputted even when the vehicle that has stopped starts traveling.

In order to achieve the second object, according to a twelfth feature ofthe present invention, there is provided a vehicular travel locusestimator comprising: a vehicle speed sensor for detecting a vehiclespeed; a yaw rate sensor for detecting a yaw rate; first travel locusestimator for estimating a future travel locus of the vehicle based onthe vehicle speed detected by the vehicle speed sensor and the yaw ratedetected by the yaw rate sensor; estimated travel locus output providingthe estimated travel locus; travel locus calculator for calculating apast travel locus of the vehicle; second travel locus estimator forestimating a future travel locus of the vehicle based on the calculatedpast travel locus; and stationary state determiner for determining thatthe vehicle is in a substantially stationary state; the estimated travellocus output providing the travel locus estimated by the second travellocus estimator when the stationary state determiner determines that thevehicle is in a substantially stationary state.

With this arrangement, when the stationary state determiner determinesthat the vehicle is in a substantially stationary state, that is, thereliability of the yaw rate outputted by the yaw rate sensor is low, theestimated travel locus output does not provide a future travel locus ofthe vehicle estimated by the first travel locus estimator using the yawrate, but instead provides a future travel locus of the vehicleestimated by the second travel locus estimator based on the past travellocus of the vehicle calculated by the travel locus calculator.Therefore, it is possible to enhance the accuracy of the future travellocus even when the vehicle that has stopped starts traveling.

According to a thirteenth feature of the present invention, in additionto the eleventh or twelfth feature, the travel locus calculator has anabsolute coordinate system that enables a subject vehicle position and asubject vehicle direction to be recorded with a given point as areference, calculates a subject vehicle direction in the absolutecoordinate system based on the yaw rate detected by the yaw rate sensor,calculates a plurality of subject vehicle positions based on thecalculated subject vehicle direction and the vehicle speed detected bythe vehicle speed sensor, and calculates the past travel locus of thevehicle from the plurality of calculated subject vehicle positions inthe absolute coordinate system.

With this arrangement, the travel locus calculator calculates thesubject vehicle direction in the absolute coordinate system based on theyaw rate detected by the yaw rate sensor, calculates the plurality ofsubject vehicle positions in the absolute coordinate system based on thesubject vehicle direction and the vehicle speed detected by the vehiclespeed sensor, and calculates the past travel locus of the vehicle fromthe plurality of subject vehicle positions. Therefore, it is possible tocalculate the past travel locus of the vehicle by employing the yaw ratesensor and the vehicle speed sensor which are also used when the firsttravel locus estimator estimates the future travel locus of the vehicle.

According to a fourteenth feature of the present invention, in additionto the eleventh or twelfth feature, the system further comprises asteering angle sensor for detecting a steering angle of the vehicle; andthe travel locus calculator has an absolute coordinate system thatenables a subject vehicle position and a subject vehicle direction to berecorded with a given point as a reference, calculates a subject vehicledirection in the absolute coordinate system based on the steering angledetected by the steering angle sensor, calculates a plurality of subjectvehicle positions based on the calculated subject vehicle direction andthe vehicle speed detected by the vehicle speed sensor, and calculatesthe past travel locus of the vehicle from the plurality of calculatedsubject vehicle positions in the absolute coordinate system.

With this arrangement, the travel locus calculator calculates thesubject vehicle direction in the absolute coordinate system based on thesteering angle detected by the steering angle sensor, calculates theplurality of subject vehicle positions in the absolute coordinate systembased on the subject vehicle direction and the vehicle speed detected bythe vehicle speed sensor, and calculates the past travel locus of thevehicle from the plurality of subject vehicle positions. Therefore, itis possible to calculate the past travel locus of the vehicle byemploying the steering angle sensor which is generally provided in avehicle.

According to a fifteenth feature of the present invention, in additionto the eleventh or twelfth feature, the system further comprises subjectvehicle position detector for detecting a subject vehicle position in anabsolute coordinate system based on a signal from outside the vehicle,and subject vehicle position memory for storing the detected subjectvehicle position; and the travel locus calculator calculates the pasttravel locus of the vehicle from a plurality of subject vehiclepositions stored by the subject vehicle position memory.

With this arrangement, the subject vehicle position memory stores thesubject vehicle position detected in the absolute coordinate system bythe subject vehicle position detector based on the signal from outsidethe vehicle, and the travel locus calculator calculates the past travellocus of the vehicle from the plurality of stored subject vehiclepositions. Therefore, it is possible to easily calculate the past travellocus of the vehicle by utilizing the output from the subject vehicleposition detector.

According to a sixteenth feature of the present invention, in additionto the thirteenth feature, the travel locus calculator calculates thepast travel locus of the vehicle by subjecting the plurality of subjectvehicle positions in the absolute coordinate system to a least-squaresprocedure.

With this arrangement, the travel locus calculator calculates the pasttravel locus of the vehicle by subjecting the plurality of subjectvehicle positions in the absolute coordinate system to a least-squaresprocedure. Therefore, it is possible to calculate the past travel locusof the vehicle with good accuracy even if there are variations, due toerrors, in the arrangement of the plurality of subject vehiclepositions.

According to a seventeenth feature of the present invention, in additionto the fourteenth feature, the travel locus calculator calculates thepast travel locus of the vehicle by subjecting the plurality of subjectvehicle positions in the absolute coordinate system to a least-squaresprocedure.

With this arrangement, the travel locus calculator calculates the pasttravel locus of the vehicle by subjecting the plurality of subjectvehicle positions in the absolute coordinate system to a least-squaresprocedure. Therefore, it is possible to calculate the past travel locusof the vehicle with good accuracy even if there are variations, due toerrors, in the arrangement of the plurality of subject vehiclepositions.

According to an eighteenth feature of the present invention, in additionto the fifteenth feature, the travel locus calculator calculates thepast travel locus of the vehicle by subjecting the plurality of subjectvehicle positions in the absolute coordinate system to a least-squaresprocedure.

With this arrangement, the travel locus calculator calculates the pasttravel locus of the vehicle by subjecting the plurality of subjectvehicle positions in the absolute coordinate system to a least-squaresprocedure. Therefore, it is possible to calculate the past travel locusof the vehicle with good accuracy even if there are variations, due toerrors, in the arrangement of the plurality of subject vehiclepositions.

The above-mentioned object, other objects, characteristics, andadvantages of the present invention will become apparent from anexplanation of preferred embodiments that will be described in detailbelow by references to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 to FIG. 4 show a first embodiment of the present invention: FIG.1 is a block diagram of a control system for an ACC system; FIG. 2 is aflowchart for explaining the operation; FIG. 3 is a diagram forexplaining the operation of first travel locus estimator; and FIG. 4 isa diagram for explaining the operation of second travel locus estimator.

FIG. 5 and FIG. 6 show a second embodiment of the present invention:FIG. 5 is a flowchart corresponding to FIG. 2; and FIG. 6 is a diagramfor explaining the operation of control object determiner.

FIG. 7 and FIG. 8 show a third embodiment of the present invention: FIG.7 is a block diagram of a control system for an ACC system; and FIG. 8is a flowchart for explaining the operation.

FIG. 9 is a block diagram of a control system for an ACC systemaccording to a fourth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A first embodiment of the present invention will be described below byreference to FIG. 1 to FIG. 4.

FIG. 1 shows an ACC (Adaptive Cruise Control) system which maintains apreset inter-vehicle distance when there is a preceding vehicle, thustracking the preceding vehicle, and maintains a preset vehicle speedwhen there is no preceding vehicle, thus keeping the speed constant. TheACC system includes: first travel locus estimator M1; travel locuscalculator M2; second travel locus estimator M3; locus correlationdegree calculator M4; control object determiner M5; control target valuedeterminer M6; and vehicle controller M7.

Connected to the first travel locus estimator M1 are a vehicle speedsensor 11 and a yaw rate sensor 12. Connected to the travel locuscalculator M2 are the vehicle speed sensor 11, the yaw rate sensor 12,and a steering angle sensor 13. Connected to the control objectdeterminer M5 is a radar device 14. Connected to the vehicle controllerM7 are a display 15, a deceleration actuator 16, and an accelerationactuator 17.

As shown in FIG. 3, the first travel locus estimator M1 estimates afuture travel locus Tn of a subject vehicle based on a vehicle speeddetected by the vehicle speed sensor 11 and a yaw rate detected by theyaw rate sensor 12. That is, since a turning radius Rn of the vehiclecan be calculated from a present vehicle speed and yaw rate, the futuretravel locus Tn of the subject vehicle can be estimated by joining anarc having the turning radius Rn to a present direction of travel of thesubject vehicle.

As shown in FIG. 4, the travel locus calculator M2 calculates anabsolute direction of the subject vehicle in an absolute coordinatesystem from the integral of the yaw rate detected by the yaw rate sensor12 or the cumulative steering angle detected by the steering anglesensor 13; and calculates at predetermined time intervals an absoluteposition of the subject vehicle in the absolute coordinate system fromthe absolute direction of the subject vehicle and the vehicle speeddetected by the vehicle speed sensor 11. A past travel locus of thesubject vehicle is obtained by calculation, that is, by subjectingabsolute positions of the subject vehicle (positions shown by □ in FIG.4) plotted in the absolute coordinate system at predetermined timeintervals to a least-squares procedure. Here, carrying out theleast-squares procedure enhances the accuracy with which the travellocus is calculated, even if an error is included in the plurality ofsubject vehicle positions plotted in the absolute coordinate system.

In this way, when the past travel locus of the subject vehicle iscalculated from the yaw rate and the vehicle speed, the yaw rate sensor12 and the vehicle speed sensor 11 for detecting the yaw rate and thevehicle speed in the first travel locus estimator M1 are used as theyare, thereby preventing any increase in the number of sensors. Further,when the past travel locus of the subject vehicle is calculated from thesteering angle, the steering angle sensor 13 which is generally providedin a vehicle is used as it is, thereby preventing any increase in thenumber of sensors.

The second travel locus estimator M3 estimates a future travel locus Toof the subject vehicle by, for example, calculating a radius ofcurvature Ro at the terminal of the past travel locus of the subjectvehicle (that is, the present subject vehicle position) and joining anarc having this radius of curvature Ro to the terminal of the pasttravel locus of the subject vehicle.

The locus correlation degree calculator M4 compares the future travellocus Tn of the subject vehicle estimated by the first travel locusestimator M1 with the future travel locus To of the subject vehicleestimated by the second travel locus estimator M3, and calculates adegree of correlation.

There are various modes for the degree of correlation; for example, adifference between the travel locus Tn estimated by the first travellocus estimator M1 and the travel locus To estimated by the secondtravel locus estimator M3 is calculated, and it can be determined thatthe smaller the difference the higher the degree of correlation.Alternatively, a degree of similarity in two-dimensional shape betweenthe travel locus Tn estimated by the first travel locus estimator M1 andthe travel locus Tn estimated by the second travel locus estimator M3 iscalculated, and it can be determined that the higher the degree ofsimilarity the higher the degree of correlation. Alternatively, aturning radius of the travel locus Tn estimated by the first travellocus estimator M1 and a turning radius of the travel locus To estimatedby the second travel locus estimator M3 are calculated, and it can bedetermined that the smaller the difference therebetween the higher thedegree of correlation.

The control object determiner M5 sets as a control object, amongpreceding vehicles detected by the radar device 14, a preceding vehiclethat is on the travel locus Tn estimated by the first travel locusestimator M1. In this process, the control object determiner M5 modifiesthe effective length of the estimated travel locus Tn, that is, thedistance up to the most distant preceding vehicle that is set as thecontrol object. That is, when the degree of correlation calculated bythe locus correlation degree calculator M4 is equal to or greater than apredetermined value, that is, when the travel locus Tn estimated by thefirst travel locus estimator M1 coincides well with the travel locus Toestimated by the second travel locus estimator M3, the effective lengthof the estimated travel locus Tn is increased from a normal set value(e.g., 100 m) to an increased value (e.g., 120 m).

When the degree of correlation calculated by the locus correlationdegree calculator M4 is less than a predetermined value, that is, whenthe travel locus Tn estimated by the first travel locus estimator M1does not coincide well with the travel locus To estimated by the secondtravel locus estimator M3, the effective length of the estimated travellocus Tn is maintained at a normal set value (e.g., 100 m). In thiscase, the effective length of the travel locus Tn may be reduced fromthe normal set value (e.g., 100 m) to a reduced value (e.g., 80 m).

In this way, if a preceding vehicle detected by the radar device 14 ispresent within the effective length of the travel locus Tn set by thecontrol object determiner M5, the preceding vehicle is determined as thecontrol object.

The control target value determiner M6 determines a target vehiclespeed, a target acceleration/deceleration, a target inter-vehicledistance, etc., which are parameters used for making the subject vehicletrack the preceding vehicle that is the control object. The vehiclecontroller M7 operates the deceleration actuator 16 or the accelerationactuator 17 based on a control target value determined by the controltarget value determiner M6 so as to make a throttle valve open or closeor operate a brake system, thus carrying out tracking control orconstant speed travel control; and displays a present control state ofthe vehicle on the display 15 so as to inform a driver.

The above operation is now further described by reference to theflowchart of FIG. 2.

Firstly in step S1 the first travel locus estimator M1 estimates thefuture travel locus Tn of the subject vehicle based on the yaw rate andthe vehicle speed. In the subsequent step S2 the travel locus calculatorM2 calculates the absolute direction of the subject vehicle in theabsolute coordinate system from the integral of the yaw rate or thecumulative steering angle. In step S3 the absolute position of thesubject vehicle in the absolute coordinate system is calculated atpredetermined time intervals from the absolute direction and the vehiclespeed. Further, in step S4 the past travel locus of the subject vehicleis calculated by subjecting the coordinates of the plurality of absolutepositions of the subject vehicle obtained at predetermined timeintervals to the least-squares procedure, and the second travel locusestimator M3 estimates the future travel locus To of the subject vehiclefrom the past travel locus of the subject vehicle.

In the subsequent step S5 the travel locus Tn estimated by the firsttravel locus estimator M1 and the travel locus To estimated by thesecond travel locus estimator M3 are compared so as to calculate thedegree of correlation between the two: if in step S6 the degree ofcorrelation is equal to or greater than the predetermined value, then instep S7 the effective length of the estimated travel locus Tn isincreased from the normal set value; and if in step S6 the degree ofcorrelation is less than the predetermined value, then in step S8 theeffective length of the estimated travel locus Tn is maintained at thenormal set value.

A second embodiment of the present invention is now described byreference to FIG. 5 and FIG. 6.

In the first embodiment, the control object determiner M5 modifies,according to the degree of correlation calculated by the locuscorrelation degree calculator M4, the effective length of the travellocus in which the control object is determined, but as shown in FIG. 6in the second embodiment the control object determiner M5 modifies,according to the degree of correlation calculated by the locuscorrelation degree calculator M4, the effective detection distance ofthe radar device 14 with which the control object is determined.

That is, when the degree of correlation calculated by the locuscorrelation degree calculator M4 is equal to or greater than apredetermined value, that is, when the travel locus Tn estimated by thefirst travel locus estimator M1 coincides well with the travel locus Toestimated by the second travel locus estimator M3, the effectivedetection distance of the radar device 14 is increased from a normal setvalue (e.g., 100 m) to an increased value (e.g., 120 m) (see step S7 ′of FIG. 5).

Further, when the degree of correlation calculated by the locuscorrelation degree calculator M4 is less than the predetermined value,that is, the travel locus Tn estimated by the travel locus estimator M1does not coincide well with the travel locus To estimated by the secondtravel locus estimator M3, the effective detection distance of the radardevice 14 is maintained at the normal set value (e.g. 100 m) (see stepS8′ of FIG. 5). In this case, the effective detection distance of theradar device 14 may be reduced from the normal set value (e.g. 100 m) toa reduced value (e.g. 80 m).

As described above, the travel locus Tn estimated from the runningconditions (vehicle speed and yaw rate) of the subject vehicle and thetravel locus To estimated from the past travel locus of the subjectvehicle are compared, and when the degree of correlation therebetween ishigh it is determined that the reliability of the travel locus Tnestimated from the running conditions of the subject vehicle is high.Therefore, it is possible to reliably determine a more distant precedingvehicle, by setting as the control object a distant preceding vehiclethat is present on the travel locus Tn, thus carrying out an accurateinter-vehicle distance control. On the other hand, when the degree ofcorrelation of the two travel loci Tn and To is low, it is determinedthat the reliability of the travel locus Tn estimated from the runningconditions of the subject vehicle is low. Therefore, it is possible toenhance the accuracy with which the preceding vehicle is determined, bynot setting as the control object a distant preceding vehicle that ispresent on the travel locus Tn.

Further, the travel locus calculator M2 calculates the past travel locusof the subject vehicle based on the plurality of subject vehiclepositions plotted in the absolute coordinate system. Therefore, thetravel locus calculator M2 becomes less susceptible to the influence oferrors due to noise of the yaw rate sensor 12, etc., so that theaccuracy with which the past travel locus of the subject vehicle iscalculated is improved. As a result, it is unnecessary to carry outfiltering in order to remove the influence of noise of the yaw ratesensor 12, thus preventing any delay in calculating the travel locus dueto a time delay accompanying filtering, so that the second travel locusestimator M3 can quickly estimate the travel locus To, thus rapidlydetermining a preceding vehicle.

A third embodiment of the present invention is now described byreference to FIG. 7 and FIG. 8.

FIG. 7 shows an ACC (Adaptive Cruise Control) system which maintains apreset inter-vehicle distance when there is a preceding vehicle, thustracking the preceding vehicle, and maintains a preset vehicle speedwhen there is no preceding vehicle, thus keeping the speed constant. TheACC system includes: first travel locus estimator M1; travel locuscalculator M2; second travel locus estimator M3; estimated travel locusoutput M14; stationary state determiner M15; detection area setter M16;obstacle extractor M17; control target value determiner M6; and vehiclecontroller M7.

Connected to the first travel locus estimator M1 are a vehicle speedsensor 11 and a yaw rate sensor 12. Connected to the travel locuscalculator M2 are the vehicle speed sensor 11, the yaw rate sensor 12,and a steering angle sensor 13. Connected to the estimated travel locusoutput M14 are the vehicle speed sensor 11 and the yaw rate sensor 12.Connected to the stationary state determiner M15 is the vehicle speedsensor 11. Connected to the obstacle extractor M17 is a radar device 14.Connected to the vehicle controller M7 are a display 15, a decelerationactuator 16, and an acceleration actuator 17.

The first travel locus estimator M1, the travel locus calculator M2, thesecond travel locus estimator M3, the control target value determinerM6, and the vehicle controller M7 have the same functions as those ofthe first embodiment.

The estimated travel locus output M14 provides one that has higheraccuracy from among a future travel locus Tn of the subject vehicleestimated by the first travel locus estimator M1 and a future travellocus To of the subject vehicle estimated by the second travel locusestimator M3. That is, if the stationary state determiner M15 determinesthat the vehicle speed detected by the vehicle speed sensor 11 issubstantially zero and thus the vehicle is in a substantially stationarystate, the estimated travel locus output M14 provides the future travellocus To of the subject vehicle estimated by the second travel locusestimator M3.

The reason therefor is that the first travel locus estimator M1estimates the future travel locus Tn of the subject vehicle based on thevehicle speed and the yaw rate, and the yaw rate is zero when thevehicle is stationary, so that an error occurs in estimating the futuretravel locus Tn of the subject vehicle. In this case, by employing thefuture travel locus To of the subject vehicle estimated by the secondtravel locus estimator M3 based on the past travel locus of the subjectvehicle, it is possible to avoid the influence of this error.

When the subject vehicle is not stationary and the vehicle speed isequal to or greater than a predetermined value, or when the yaw rateoutputted by the yaw rate sensor 12 is stable even if the vehicle speedis less than the predetermined value, the estimated travel locus outputM14 provides the future travel locus Tn of the subject vehicle estimatedby the first travel locus estimator M1.

The reason therefor is that, when the vehicle speed is equal to orgreater than the predetermined value, the accuracy of the output of theyaw rate sensor 12 is guaranteed, so that the accuracy of the futuretravel locus Tn of the subject vehicle estimated by the first travellocus estimator M1 using the yaw rate is guaranteed. Even when thevehicle speed is less than the predetermined value, if the output of theyaw rate sensor 12 is stable, the accuracy of the future travel locus Tnof the subject vehicle estimated by the first travel locus estimator M1using the yaw rate is guaranteed.

When the subject vehicle is not stationary but the vehicle speed is lessthan the predetermined value, and the yaw rate outputted by the yaw ratesensor 12 is unstable, the estimated travel locus output M14 providesthe future travel locus To of the subject vehicle estimated by thesecond travel locus estimator M3.

As described above, when the reliability of the detected yaw rate ishigh, the accuracy of the future travel locus Tn of the subject vehicleestimated by the first travel locus estimator M1 is higher than theaccuracy of the future travel locus To of the subject vehicle estimatedby the second travel locus estimator M3. Therefore, it is possible toenhance the overall accuracy with which the travel locus is estimated,by preferentially outputting the future travel locus Tn of the subjectvehicle estimated by the first travel locus estimator M1. When the yawrate cannot be detected or the reliability of the detected yaw rate islow, the accuracy of the future travel locus To of the subject vehicleestimated by the second travel locus estimator M3 is higher than thefuture travel locus Tn of the subject vehicle estimated by the firsttravel locus estimator M1. Therefore, it is possible to enhance theoverall accuracy with which the travel locus is estimated, bypreferentially outputting the future travel locus To of the subjectvehicle estimated by the second travel locus estimator M3.

The detection area setter M16 sets a detection area having apredetermined width along a central line which is the future travellocus of the subject vehicle outputted by the estimated travel locusoutput M14. The radar device 14 transmits electromagnetic waves such asa laser beam or milli-waves, and receives reflected waves which are theelectromagnetic waves reflected from an object, thereby detecting thedirection of the object, the distance to the object, the relative speedof the object, etc. The obstacle extractor M17 extracts, from among theobjects detected by the radar device 14, an object that is presentwithin the detection area as the preceding vehicle (obstacle) which is acontrol object.

While setting the preceding vehicle extracted by the obstacle extractorM17 as the control object, the control target value determiner M6determines, a target vehicle speed, a target acceleration/deceleration,a target inter-vehicle distance, etc. which are parameters for makingthe subject vehicle track the preceding vehicle. The vehicle controllerM7 operates the deceleration actuator 16 or the acceleration actuator 17based on the control target values determined by the control targetvalue determiner M6 so as to make a throttle valve open or close oroperate a brake system, thus carrying out tracking control or constantspeed travel control; and displays the present control state of thevehicle on the display 15, thus informing a driver thereof.

The above operation related to estimation of the future travel locus ofthe subject vehicle is now further described by reference to theflowchart of FIG. 8.

Firstly in step S1′ the first travel locus estimator M1 estimates thefuture travel locus Tn of the subject vehicle based on the yaw rate andthe vehicle speed. In the subsequent step S2′ the travel locuscalculator M2 calculates an absolute direction of the subject vehicle inan absolute coordinate system from the integral of the yaw rate or thecumulative steering angle. In step S3′ an absolute position of thesubject vehicle in the absolute coordinate system is calculated atpredetermined time intervals from the absolute direction and the vehiclespeed, and further in step S4′ the coordinates of a plurality ofabsolute positions of the subject vehicle obtained at predetermined timeintervals are subjected to a least-squares procedure so as to calculatethe past travel locus of the subject vehicle, and the second travellocus estimator M3 estimates the future travel locus To of the subjectvehicle from the past travel locus of the subject vehicle.

If in the subsequent step S5′ the subject vehicle is stationary, then instep S8′ the future travel locus To of the subject vehicle estimated bythe second travel locus estimator M3 is outputted. On the other hand,even if in step S5′ the subject vehicle is not stationary, when in stepS6′ the vehicle speed is less than the predetermined value and in stepS7′ the yaw rate is not stable, then in step S8′ the future travel locusTo of the subject vehicle estimated by the second travel locus estimatorM3 is similarly outputted.

If in step S6′ the vehicle speed is equal to or greater than thepredetermined value or in step S7′ the yaw rate is stable, then in stepS9′ the future travel locus Tn of the subject vehicle estimated by thefirst travel locus estimator M1 is outputted.

A fourth embodiment of the present invention is now described byreference to FIG. 9.

In the third embodiment the vehicle speed sensor 11, the yaw rate sensor12, and the steering angle sensor 13 are connected to the travel locuscalculator M2, but in the fourth embodiment subject vehicle positionmemory M10 connected to a navigation system 18 is connected to travellocus calculator M2.

Since the navigation system 18 is capable of successively detectingsubject vehicle positions, the subject vehicle position is stored in thesubject vehicle position memory M10 at predetermined time intervals, andthe travel locus calculator M2 can calculate a past travel locus of thesubject vehicle from a plurality of past subject vehicle positionsstored in the subject vehicle position memory M10.

Other arrangements and effects of the fourth embodiment are the same asthose of the above-mentioned third embodiment.

Although embodiments of the present invention have been described above,the present invention can be modified in a variety of ways withoutdeparting from the subject matter of the present invention.

For example, an ACC system has been described in the embodiments, butthe present invention is not limited to the ACC system and is applicableto a vehicular travel locus estimation system or a vehicular controlobject determination system for any purpose.

Furthermore, the subject vehicle position detector is not limited to thenavigation system 18 of the embodiment, and may be a road-vehiclecommunication system such as a beacon.

1. A vehicular control object determination system comprising: an object detector detecting an object that is present in the direction of travel of a vehicle; a vehicle speed sensor detecting a vehicle speed; a yaw rate sensor detecting a yaw rate; a first travel locus estimator operatively coupled to the vehicle speed sensor and the yaw rate sensor, the first travel locus estimator estimating a future travel locus of the vehicle based on the vehicle speed detected by the vehicle speed sensor and the yaw rate detected by the yaw rate sensor; a control object determiner determining a control object based on a detection result obtained by the object detector, a travel locus estimated by the first travel locus estimator, and predetermined control object determination conditions; a travel locus calculator calculating a past travel locus of the vehicle; a second travel locus estimator estimating a future travel locus of the vehicle based on the calculated past travel locus; and a locus correlation degree calculator determining a degree of correlation between the travel locus estimated by the first travel locus estimator and the travel locus estimated by the second travel locus estimator; the control object determiner modifying the control object determination conditions based on an output of the locus correlation degree calculator.
 2. The vehicular control object determination system according to claim 1, wherein the control object determiner determines as a control object an object detected by the object detector if the relative distance between the position of the object and the travel locus estimated by the first travel locus estimator is equal to or less than a predetermined value, and modifies, based on the degree of correlation calculated by the locus correlation degree calculator, an effective length of the travel locus estimated by the first travel locus estimator.
 3. The vehicular control object determination system according to claim 2, wherein the control object determiner increases the effective length of the estimated travel locus when the degree of correlation calculated by the locus correlation degree calculator is equal to or greater than a predetermined value.
 4. The vehicular control object determination system according to claim 2, wherein the control object determiner reduces the effective length of the estimated travel locus when the degree of correlation calculated by the locus correlation degree calculator is less than a predetermined value.
 5. The vehicular control object determination system according to claim 1, wherein the control object determiner determines as a control object an object detected by the object detector if the distance between the subject vehicle and the position of the object is equal to or less than an effective detection distance, and modifies the effective detection distance based on the degree of correlation calculated by the locus correlation degree calculator.
 6. The vehicular control object determination system according to claim 5, wherein the control object determiner increases the effective detection distance when the degree of correlation calculated by the locus correlation degree calculator is equal to or greater than a predetermined value.
 7. The vehicular control object determination system according to claim 5, wherein the control object determiner reduces the effective detection distance when the degree of correlation calculated by the locus correlation degree calculator is less than a predetermined value.
 8. The vehicular control object determination system according to claim 1, wherein the locus correlation degree calculator calculates a degree of correlation based on a difference between the travel locus estimated by the first travel locus estimator and the travel locus estimated by the second travel locus estimator.
 9. The vehicular control object determination system according to claim 1, wherein the locus correlation degree calculator calculates the degree of correlation based on a degree of similarity in two-dimensional shape between the travel locus estimated by the first travel locus estimator and the travel locus estimated by the second travel locus estimator.
 10. The vehicular control object determination system according to claim 1, wherein the locus correlation degree calculator calculates the degree of correlation based on a difference between a first turning radius of the travel locus estimated by the first travel locus estimator and a second turning radius of the travel locus estimated by the second travel locus estimator. 11-23. (canceled) 